I think this was never going to turn out well. London broil is a lean cut of meat. The leaner the meat, the more rare you need to go IMHO. 138 is pretty high already and on top of that you seared it so it probably went into the 140s. Next time try 131 and go a little longer maybe 24 hrs.
Like mentioned above don't marinade and don't cook meats in a "bath" while sous vide. Anytime I do a roast or something else in that style, I rub the meat (usually SP) and add aromatics (shallot, crushed garlic, herbs (rosemary and thyme are my go to's)) and just add to the water bath. I personally do my roasts at 128-131 depending on what 'im going for and will sear after, whether on grill or cast iron with butter bath.
But high temp, lean cut, marinade, sear, all those factors may have worked against you. Good luck and hope you try it again. It really is simple once you get the hang of it! Try a chuck or round next, but go minimum 24-30 hrs. IMHO 30-36 is the sweet spot for a medium to large roast.